Illumination system including tunable light engine

Abstract

A tunable illumination system is disclosed which splits a single channel output into three by means of current steering and/or time division and multiplexing techniques. More particularly, the tunable light system may split the input current into three pulse-width modulated (PWM) channels. The individual duty cycles of the PWM channels may be adjusted based on a control signal that is received via a control signal interface. The control signal interface may include a switch and/or other circuity that is manipulated by the user when the user wants to change the color of light that is output by the illumination system.

What is claimed is: 
     
       1. A system comprising:
 a control signal interface configured to provide a control signal; 
 a light engine communicatively coupled to the control signal interface, the light engine comprising:
 a first signal generator configured to provide a first pulse-width modulated (PWM) signal to an input of a first switch based on the control signal, the first signal generator having a first cutoff voltage at which the first PWM signal has a 0% duty cycle when the control signal reaches the first cutoff voltage; 
 a second signal generator configured to provide a second PWM signal to an input of a second switch based on the control signal and a reference signal, the second signal generator having a second cutoff voltage at which the second PWM signal has a 0% duty cycle when the control signal reaches the second cutoff voltage, at least one of the reference signal, the first cutoff voltage, and the second cutoff voltage set such that only one of the first PWM signal and the second PWM signal is at a logic high value concurrently; and 
 a NOR gate configured to receive the first PWM signal and the second PWM signal as inputs and provide a third PWM signal to an input of a third switch. 
 
 
     
     
       2. The system of  claim 1 , wherein:
 the second signal generator is configured to provide the second PWM signal based on a value proportional to a combination of the reference signal minus the control signal. 
 
     
     
       3. The system of  claim 1 , further comprising:
 an operational amplifier having a first input coupled to receive an inverted input of the control signal, a second input coupled to receive a non-inverting input of the reference signal, and an output configured to supply an output operational amplifier signal to the second signal generator and an inverted signal to the first input. 
 
     
     
       4. The system of  claim 3 , further comprising:
 a reference voltage generator configured to generate an initial reference signal; and 
 a voltage divider configured to divide the initial reference signal to provide the reference signal. 
 
     
     
       5. The system of  claim 4 , wherein:
 the voltage divider comprises a first resistor between the reference voltage generator and the second input of the operational amplifier and a second resistor between the second input of the operational amplifier and ground, the first resistor having a first resistance and the second resistor having a second resistance, and 
 the control signal is supplied to the first input of the operational amplifier through a third resistor having the first resistance and the output operational amplifier signal is connected to the first input of the operational amplifier through a fourth resistor having the second resistance. 
 
     
     
       6. The system of  claim 5 , wherein a ratio of the second resistance to the first resistance is configured to determine a rate at which a brightness of a light source connected to the second switch changes. 
     
     
       7. The system of  claim 1 , further comprising:
 a first light emitting diode (LED) coupled to the first switch and configured to emit light of a first color; 
 a second LED coupled to the second switch and configured to emit light of a second color; and 
 a third LED coupled to the third switch and configured to emit light of a third color. 
 
     
     
       8. The system of  claim 7 , wherein:
 the reference signal, the first cutoff voltage, and the second cutoff voltage are set to control a first duty cycle of the first PWM signal, a second duty cycle of the second PWM signal, and a third duty cycle of the third PWM signal to provide a correlated color temperature (CCT) based on a user input that sets the control signal. 
 
     
     
       9. The system of  claim 8 , wherein:
 the control signal is a digital representation of a number or an alphanumerical string that indicates the CCT. 
 
     
     
       10. The system of  claim 1 , wherein:
 the reference signal, the first cutoff voltage, and the second cutoff voltage are set to control a first duty cycle of the first PWM signal, a second duty cycle of the second PWM signal, and a third duty cycle of the third PWM signal such that as the control signal changes: one of the first and second duty cycles is 0% concurrently as each of the third duty cycle and another of the first and second duty cycles varies from 0% to 100%, and a total of the first, second, and third duty cycles is 100%. 
 
     
     
       11. The system of  claim 10 , wherein:
 the reference signal, the first cutoff voltage, and the second cutoff voltage are set such that as the control signal increases: 
 the first duty cycle decreases linearly from 100% to 0% and the third duty cycle increases linearly from 0% to 100%, and 
 at the control signal at which the first duty cycle first reaches 0%, the second duty cycle starts to increase linearly from 0% to 100% and the third duty cycle starts to decrease linearly from 100% to 0%. 
 
     
     
       12. The system of  claim 10 , wherein:
 the reference signal, the first cutoff voltage, and the second cutoff voltage are set such that as the control signal increases: 
 the first duty cycle decreases linearly from 100% to 0% and the third duty cycle increases linearly from 0% to 100%, 
 the first duty cycle reaches 0% at a first control signal, and 
 the second duty cycle starts to increase linearly from 0% to 100% and the third duty cycle starts to decrease linearly from 100% to 0% at a second control signal larger than the first control signal. 
 
     
     
       13. The system of  claim 1 , wherein:
 the control signal interface is communicatively coupled to receive an input from an actuator; and 
 the light engine further comprises a controller communicatively coupled to receive a user input from the control signal interface and provide the control signal based thereon. 
 
     
     
       14. A method comprising:
 generating a first pulse-width modulated (PWM) signal based on a control signal, the first PWM signal having a 0% duty cycle when the control signal reaches a first cutoff voltage; 
 generating a second PWM signal based on the control signal and a reference signal, the second PWM signal having a 0% duty cycle when the control signal reaches a second cutoff voltage; 
 setting at least one of the reference signal, the first cutoff voltage, and the second cutoff voltage such that only one of the first PWM signal and the second PWM signal is at a logic high value concurrently; 
 generating a third PWM signal based on a NOR combination of the first PWM signal and the second PWM signal; and 
 driving a first, a second, and a third light emitting diode (LED) respectively using the first, second, and third PWM signals, each of the first, second, and third LED configured to emit light of a different color. 
 
     
     
       15. The method of  claim 14 , further comprising:
 controlling a first duty cycle of the first PWM signal, a second duty cycle of the second PWM signal, and a third duty cycle of the third PWM signal using the reference signal, the first cutoff voltage, and the second cutoff voltage to provide a correlated color temperature (CCT) based on a user input that sets the control signal. 
 
     
     
       16. The method of  claim 15 , further comprising:
 providing the control signal as a digital representation of a number or an alphanumerical string that indicates the color blend or CCT. 
 
     
     
       17. The method of  claim 14 , further comprising:
 setting the reference signal, the first cutoff voltage, and the second cutoff voltage to control a first duty cycle of the first PWM signal, a second duty cycle of the second PWM signal, and a third duty cycle of the third PWM signal such that as the control signal changes:
 one of the first and second duty cycles is 0% concurrently as each of the third duty cycle and another of the first and second duty cycles varies from 0% to 100%, and 
 a total of the first, second and third duty cycles is 100%. 
 
 
     
     
       18. The method of  claim 17 , further comprising:
 setting the reference signal, the first cutoff voltage, and the second cutoff voltage such that as the control signal increases:
 the first duty cycle decreases linearly from 100% to 0% and the third duty cycle increases linearly from 0% to 100%, and 
 at the control signal at which the first duty cycle first reaches 0%, the second duty cycle starts to increase linearly from 0% to 100% and the third duty cycle starts to decrease linearly from 100% to 0%. 
 
 
     
     
       19. The method of  claim 17 , further comprising:
 setting the reference signal, the first cutoff voltage, and the second cutoff voltage such that as the control signal increases:
 the first duty cycle decreases linearly from 100% to 0% and the third duty cycle increases linearly from 0% to 100%, 
 the first duty cycle reaches 0% at a first control signal, and 
 the second duty cycle starts to increase linearly from 0% to 100% and the third duty cycle starts to decrease linearly from 100% to 0% at a second control signal larger than the first control signal. 
 
 
     
     
       20. A device comprising:
 a current source configured to provide a current to a first, a second, and a third output; 
 a first signal generator configured to provide a first pulse-width modulated (PWM) signal to an input of a first switch based on a variable control signal provided via a user input, the first signal generator having a first cutoff voltage at which the first PWM signal has a 0% duty cycle when the control signal reaches the first cutoff voltage, the first switch connected with a first input and configured to provide a path to ground when the first input and output are electrically connected; 
 a second signal generator configured to provide a second PWM signal to an input of a second switch based on the control signal and a reference signal, the second signal generator having a second cutoff voltage at which the second PWM signal has a 0% duty cycle when the control signal reaches the second cutoff voltage, at least one of the reference signal, the first cutoff voltage, and the second cutoff voltage set such that only one of the first PWM signal and the second PWM signal is at a logic high value concurrently, the second switch connected with a second input and configured to provide a path to ground when the second input and output are electrically connected; and 
 a NOR gate configured to receive the first PWM signal and the second PWM signal as inputs and provide a third PWM signal to an input of a third switch, the third switch connected with a third input and configured to provide a path to ground when the third input and output are electrically connected. 
 
     
     
       21. The device of  claim 20 , further comprising:
 an operational amplifier having a first input coupled to receive an inverted input of the control signal, a second input coupled to receive a non-inverting input of the reference signal, and an output configured to supply an output operational amplifier signal to the second signal generator and an inverted signal to the first input. 
 
     
     
       22. The device of  claim 21 , further comprising:
 a reference voltage generator configured to generate an initial reference signal; and 
 a voltage divider configured to divide the initial reference voltage to provide the reference signal, the voltage divider comprising a first resistor between the reference voltage generator and the second input of the operational amplifier and a second resistor between the second input of the operational amplifier and ground, the first resistor having a first resistance and the second resistor having a second resistance, the control signal supplied to the first input of the operational amplifier through a third resistor having the first resistance and the output operational amplifier signal is connected to the first input of the operational amplifier through a fourth resistor having the second resistance.